The present invention relates to data storage systems. More specifically, the present invention relates to data storage systems using read heads which utilize the giant magnetoresistive (GMR) effect.
Magnetic sensors utilizing the GMR effect, frequently referred to as xe2x80x9cspin valvexe2x80x9d sensors, are known in the art. A spin valve sensor is typically a sandwiched structure consisting of two ferromagnetic layers separated by a thin non-ferromagnetic layer. One of the ferromagnetic layers is called the xe2x80x9cpinned layerxe2x80x9d because it is magnetically pinned or oriented in a fixed and unchanging direction. Magnetic pinning of the pinned layer is frequently accomplished using an adjacent antiferromagnetic layer, commonly referred to as the xe2x80x9cpinning layer,xe2x80x9d through exchange coupling. The pinned layer must be kept magnetically rigid at a device operating temperature, of about 150xc2x0 C. in a disc drive where an excitation field as high as 300 Oe is applied to the sensor. The other ferromagnetic layer is called the xe2x80x9cfreexe2x80x9d or xe2x80x9cunpinnedxe2x80x9d layer because the magnetization is allowed to rotate in response to the presence of external magnetic fields. Spin valve/GMR sensors provide an output which is dependent upon angle variation of the magnetizations between the free and pinned layers.
One type of self pinned layer is known in the art as an artificial antiferromagnetic layer (AAF) or a synthetic antiferromagnetic layer (SAF). Such a SAF layer is formed by three sub-layers, a first ferromagnetic layer, a second ferromagnetic layer and a non-magnetic spacer layer separating the two ferromagnetic layers. The two ferromagnetic layers have magnetic vectors which are biased in antiparallel directions and in the plane of the sensor (perpendicular to the air bearing surface). This is described in, for example, U.S. Pat. No. 5,583,725, issued Dec. 10, 1996 to Coffey et al., entitled xe2x80x9cSPIN VALVE MAGNETORESISTIVE SENSOR WITH SELF-PINNED LAMINATED LAYER AND MAGNETIC RECORDING SYSTEM USING THE SENSOR, which is incorporated herein by reference.
An Co/Ru/Co SAF layer has been used in combination with an NiO antiferromagnetic layer in a spin valve. See for example, R. E. Fontana, U.S. Pat. No. 5,701,223 entitled A SPIN VALVE MAGNETORESISTIVE SENSOR WITH ANTIPARALLEL PINNED LAYER AND IMPROVED EXCHANGE BIAS LAYER, AND MAGNETIC RECORDING SYSTEM USING THE SAME. An apparent purpose of combining the Co/Ru/Co SAF layer with the NiO antiferromagnetic layer was to reduce the demag field from the pinned layer in order to optimize the bias point of the sensor. An additional benefit was the enhancement of the pinning/switching field. However, the thermal relaxation in a NiO spin valve is severe due to the low blocking temperature (approximately 200xc2x0 C.) and poor blocking temperature distribution. This spin valve structure lacks stability, and is therefore not ideal for a read sensor. FIG. 1 is a plot illustrating the temperature dependence of such a spin valve having an NiO antiferromagnetic layer and a SAF pinned layer. As can be seen in FIG. 1, this spin valve structure exhibits poor thermal stability. Further, the GMR transfer curves (plotting resistance of the sensor as a function of applied magnetic field) exhibit a permanent change after experiencing a thermal temperature ramp.
Disclosed are a spin valve magnetoresistive sensor and methods of fabricating the same. The sensor includes a free layer, a synthetic antiferromagnetic (SAF) layer, a spacer layer positioned between the free layer and the SAF layer, and a Mn-based antiferromagnetic pinning layer with a high blocking temperature in contact with the SAF layer. For example, a NiMn layer having a blocking temperature of approximately 400xc2x0 C. or a PtMn layer having a blocking temperature of approximately 380xc2x0 C. can be used. The SAF layer includes first and second ferromagnetic CoFe layers and an Ru spacer layer positioned between and directly in contact with the first and second CoFe ferromagnetic layers.